Automatic draft compensation for reversing mill edger drive

ABSTRACT

An edger mill velocity reference signal is developed as a function of the draft which occurs during the forward or odd pass through a reversing mill where the entry thickness of the material to be rolled is set during the reverse or even pass of the mill. The draft compensation necessary to adjust the edger drive speed is obtained, in the preferred embodiment, by computing the ratio of the reverse pass screwdown position to the following forward pass screwdown position.

United States Patent [191 11 3,739,613 Gripp et al. 1 June 19, 1973AUTOMATIC DRAFT COMPENSATION FOR Primary ExaminerMilton S. MehrREVERSING MILL EDGER DRIVE AIt0rney-F. H. Henson, R. G. Brodahl and J.J. Wood [75] Inventors: Leonard P. Gripp; Norman L.

Kincaid; Melvin A. Hensleigh, all of Buffalo, NY. ABSTRACT Assignee?Westinghouse Elecn'ic Cflrporafion, An edger mill velocity referencesignal is developed as Plttsburgh, Pa. a function of the draft whichoccurs during the forward [22] Filed: 9 1972 or odd pass through areversing mill where the entry thickness of the material to be roiled isset during the PP 224,393 reverse or even pass of the mill. The draftcompensation necessary to adjust the edger drive speed is 0b- 52 U.S.c1. 72/19, 72/21 mined, in the Preferred embodiment, by Computing the 51Int. Cl B2lb 37/00 ratio reverse Pass screwdow Position the [58] Fieldof Search 72/6, 8, 21, 19 Owing forward PasS screwdow Posifim [56]References Cited UNITED STATES PATENTS 3,363,441 1/1968 Smith, Jr 72/8 9Claims, 2 Drawing Figures 7 3,543,548 12/1970 Smith, Jr 72/7 EDGE M n Sd"zHd I Ve-- u He i l -Hd it I EDGER DRIVE DELIVERY [3O SPEED TRANSDUCERVM ref v Hd AUTOMATIC MANUAL REFERENCE DRAFT Q0 CONTROL MIXER SCOMPENSAT'ON 2 A VEref F/R ROLL DIAMETER lad COMPENSATION SEQUENCE ISOCONTROL PATENTED 9 3.739 .613

EDQEB MAIN MILL I n Sd EHd I ev Vd- He/ I H I I EDGER I DRIvE DELIVERYI30 sPEED TRANSDUCER VMref vd Hd I20] MANUAL REFERENCE EQXI A TICCONTROL M'XER COMPENSATION VEref F/R ROLL DIAMETER COMPENSATION SEQUENCEIso CONTROL Vd sagas S EHe M ANALOG MEMORY) 243 I RESET POSITION 2'0 Ix2 D I f-@- DRIVER l REsET sIGNAL I I Fe*He I I L RESET I VEIIefAUTOMATIC DRAFT COMPENSATION FOR REVERSING MILL EDGER DRIVE BACKGROUNDOF THE INVENTION In the process of rolling metal plate or other materialseveral passes must be made through a main mill to reduce the height ofthe material and, at the same time, edge rolling may be required eitherto reduce the width or to hold a previously established width. Thisprocess may be carried out in a reversing horizontal mill where bothedge and height rollings are performed during forward or odd passes,with the edge rollers preceding the horizontal or main mill rollers. Theforward passes are sometimes referred to as odd passes since the firstpass is forward and the second pass and even passes thereafter are inthe reverse direction.

After each reverse or even pass, the edging mill speed must be adjustedfor what has been referred to in the art as draft compensation due tothe change in the material thickness as it passes through the mill inthe forward direction. This change in thickness causes a correspondingchange in plate speed. In existing reversing mill control systems, anoperator periodically sets an initial edger speed rheostat to a nominaldraft compensation setting. This setting provides a reasonably accuratedraft compensation reference for some forward passes but it has beenfound that either forward or odd passes are then performed with errorsexisting in the draft compensation. The operator does not have timebetween passes to properly calculate and adjust the draft compensationreference signal to account for the change in edger velocity whichshould be made. As a result, there is a velocity mismatch between theedger mill drive speed and the main mill entrance speed with the resultthat the edger drive may attempt to push the product to the main mill ormay attempt to pull the product from the main mill with the result thatthe edger motor current is either higher or lower than desired.

SUMMARY OF THE INVENTION The edger drive speed reference isautomatically adjusted during each forward pass to compensate for thedraft which occurs during the forward pass. A system is provided where arepresentation of the mill delivery thickness (Hd) produced during aneven pass becomes the edger entry thickness (He) for the next odd passand the draft compensation then is automatically generated as theproduct of the mill delivery speed (Vd) times the ratio of PM to He.This then provides an edger velocity reference signal which continuouslyvaries to adjust the edger speed so that it is approximately equal tothe main mill entry speed for the particular delivery speed occurringfor a certain draft. The automatic control relationship satisfied by theinvention may then be expressed as:

VEref= Vd Hd/He.

In the preferred embodiment of the invention, a representation of heightHd is continuously developed by reading the screwdown setting of themain mill which differs from the desired height measurement only by millstretch which is relatively small. The height or thickness representingsignal then is stored in an analog memory (which could be a digitalmemory in an equivalent digital system) during each even pass and thenis used as a representation of the entry thickness I-Ie during thefollowing odd pass to develop the ratio corresponding to Hd/He, wherethe Hd representation is continuously read during the forward pass toprovide continuous draft compensation adjustment in the reference signalVEref during the forward pass. When the screwdown positionrepresentation is used as the approximation of height or thickness, thedraft compensation ratio then becomes Sd/Se where Sd and Se correspondto Hd and He, respectively.

The above and other objects and features of the invention will becomeapparent from the following detailed description taken in connectionwith the accompanying drawings which form a part of this specification,and in which:

FIG. 1 shows a system employing an automatic draft compensator providedaccording to the invention; and

FIG. 2 is a schematic diagram of one form of automatic draft compensatoras utilized in the system of FIG. 1.

Referring now to FIG. I, it will be noted that a strip or plate 1 passesbetween edger rolls 2, only one of which is visible in FIG. 1, to mainmill rolls 3. The edger exit velocity VE should be equal to the mainmill entry velocity if proper draft compensation adjusts VE as will bedescribed in detail below. Edger rolls 2 are driven by a suitable drivewhich receives a mixed reference signal VMref from a reference mixerwhich receives the reference signal VEref provided by automaticdraft-compensator 200. Compensator 200 functions on the basis of thedelivery speed Vd provided by a transducer which is suitably coupled torolls 3 to derive a representation of the circumferential velocitythereof. A representation of the delivery thickness or height Hd isderived through a screwdown position signal generator which may formpart of the screwdown control mechanism (not shown) associated with themain mill. Such apparatus is now well known in the art and, accordingly,is not shown or discussed herein. The representation of deliverythickness may be made directly on the strip but in this case a separatemeasurement must be made to determine the entry thickness He as will bediscussed below. A sequence control is shown as providing a switchingsignal F/R which rep resents forward and reverse passes. Control 150 mayform part of a computer system and may provide many other sequencecontrol signals utilized throughout the entire milling process. Onlysignal F/R is of importance herein.

As shown in FIG. 2, compensator 200 receives screwdown signal Sdrepresenting delivery thickness Hd during both forward and reversepasses. Signal Sd is ap plied both to a switch X1 shown in the openposition and to a difference amplifier 210, the function of which willbe explained below. The open position of switch X1 corresponds to theforward representation of the sequence control so that, during a forwardpass, signal Sd is applied only to difference amplifier 210. During areverse pass, switch X1 is closed and analog memory 220 (which may bereplaced with a suitable digital equivalent) stores a representation ofSd, during the reverse pass, on a capacitor C220. During forward passesswitch X1 opens under control of signal F/R and analog memory 220 holdsthe previous screwdown position which then represents the entry heightHe for the next pass. Thus, during a forward pass, signal Sd representsthe screwdown position during the forward pass which was applied todifference amplifier 210. The output of analog memory 220 (referenced asSm) provides the representation of the entry thickness He. It may benoted that the equivalent function of memory 220 would be to actuallymeasure He during the forward pass but this would require additionalhardware and, accordingly, the shared use of the screwdownrepresentation Sd to provide both representations He and Hd is preferredin the practice of the invention. During a reverse pass when switch X1is closed to develop a representation of height He, 8. second switch X2is open and driver 230 receives a signal to reset a motorizedpotentiometer system including a motor 241, a first potentiometer 242,which receives the representation of He, and a second potentiometer 243also driven by motor 241, which receives a suitable constantproportionality signal K. Potentiometers 242 and 243 will be referred toas the E and D potentiometers, respectively. Both potentiometers D and Eare reset to an initial position by the reset signal during reversepasses so that at the beginning of a forward pass, potentiometer Ereceives the He representation and provides a tapped signal representedas FE*He to signify that a signal derived thereof is the function of theposition (FE) of potentiometer E and signal He applied thereto. It willbe assumed in the following discussion that FE varies from 1 at thereset position to zero as potentiometer E is driven to the other extremefrom the reset position. The output signal produced by differenceamplifier 210 during a forward pass then may be represented as: ER HdFE*He. During the forward pass, switch X2 is in the upper position shownand consequently driver 230 will move both potentiometers D and E fromtheir initial reset position until signal ER becomes zero. When thisoccurs, the setting of potentiometer E may then be derived from thefollowing:

ER O Hd- FE*He FE*He Hd FE Hd/He.

It may be seen, then, that the desired correction ratio is provided bythe position of potentiometer E. However, the signal provided bypotentiometer E after the error signal is zero must correspond to Hd anddoes not, therefore, provide the desired signal. Accordingly,potentiometer D is employed to develop a suitable representation ofK*Hd/He which is applied to an analog multiplier 250 also receivingsignal Vd from transducer 130 of FIG. 1. It may be seen, then, thatoutput signal VEref produced by multiplier 250 may be defined as:

VEref= (K*Hd/He) Vd,

so that, during forward passes, the edger reference signal VErefiscontinuously adjusted as a function of the delivery velocity Vd timesthe ratio of delivery thickness Hd to entry thickness He.

Reference is again made to FIG. 1 where it will be noted that referencemixer 120 may receive other control signals represented as manualcontrol, roll diameter compensation, and a sequence control signal, notdefined. The precise function of mixer 120 will not be considered hereinsince it does not form a part of the invention. Signal VMref, however,is developed as a function of VEref during forward passes and that it isVEref which provides the automatic draft compensation according to theinvention.

It will be understood that while an analog system has been presented toillustrate one embodiment of the invention, the particular compensatingrelationships described herein may be developed by means of a digitalcomputer. Other variations in the general technique taught by theinvention for developing the compensating edger drive reference signalwill be apparent to those skilled in the art.

We claim as our invention:

1. In a reversing mill wherein material to be rolled is moved forwardduring odd passes through edger rolls for width control and is moved inreverse during even passes without width control, an automatic draftcompensating system comprising: first means for producing a first signalrepresenting main mill delivery thickness during forward passes; secondmeans for producing a second signal representing the delivery thicknessof said main mill during even passes, said second signal thenrepresenting the entry thickness for the following odd passes; thirdmeans, operative during odd passes, for producing a draft correctionsignal proportional to the ratio of said first signal to said secondsignal; and fourth means responsive to a signal representing main milldelivery speed and to said draft correction signal for producing anedger velocity reference signal.

2. The automatic draft compensating system of claim 1 wherein saidsecond means includes a memory operated during reverse passes to producea signal representing the entry thickness for the next following forwardpass.

3. The automatic draft compensating system of claim 2 wherein saidmemory is an analog memory including a capacitor for storing a signalrepresenting said entry thickness.

4. The automatic draft compensating system of claim 1 wherein said firstmeans produces a representation of delivery thickness during a forwardpass as a function of the reversing mill screwdown position during aforward pass and said second means including a memory for producing arepresentation of the entry thickness of material as a function of thescrewdown position during the reverse passes.

5. The automatic draft compensating system of claim 1 wherein said thirdmeans includes a difference amplifier for generating an error signalinitially set to represent the difference between said first and secondsignals and further includes means for determining the fraction of saidsecond signal that must be applied to said difference amplifier toreduce said error to zero.

6. In combination, an edger roller drive for establishing an edgervelocity Ve, main mill speed transducing means for producing arepresentation of main mill delivery speed Vd and mill deliverythickness Hd, a sequence control for producing a signal F/R representingforward and reverse mill passes, and automatic draft compensation meansresponsive to signal Hd, F/R and Vd for producing an edger velocityreference signal VEref for forward passes.

7. The combination of claim 6 wherein said automatic draft compensationmeans produces signal VEref according to the function:

VEref Vd*Hd/He,

where He is a signal representing entry thickness for a forward pass andHd represents the forward pass delivery thickness.

Sd measured in the main mill, with the memory of the screwdown positionsignal produced during a reverse pass providing the representation of Hefor the follow ing forward pass.

1. In a reversing mill wherein material to be rolled is moved forwardduring odd passes through edger rolls for width control and is moved inreverse during even passes without width control, an automatic draftcompensating system comprising: first means for producing a first signalrepresenting main mill delivery thickness during forward passes; seCondmeans for producing a second signal representing the delivery thicknessof said main mill during even passes, said second signal thenrepresenting the entry thickness for the following odd passes; thirdmeans, operative during odd passes, for producing a draft correctionsignal proportional to the ratio of said first signal to said secondsignal; and fourth means responsive to a signal representing main milldelivery speed and to said draft correction signal for producing anedger velocity reference signal.
 2. The automatic draft compensatingsystem of claim 1 wherein said second means includes a memory operatedduring reverse passes to produce a signal representing the entrythickness for the next following forward pass.
 3. The automatic draftcompensating system of claim 2 wherein said memory is an analog memoryincluding a capacitor for storing a signal representing said entrythickness.
 4. The automatic draft compensating system of claim 1 whereinsaid first means produces a representation of delivery thickness duringa forward pass as a function of the reversing mill screwdown positionduring a forward pass and said second means including a memory forproducing a representation of the entry thickness of material as afunction of the screwdown position during the reverse passes.
 5. Theautomatic draft compensating system of claim 1 wherein said third meansincludes a difference amplifier for generating an error signal initiallyset to represent the difference between said first and second signalsand further includes means for determining the fraction of said secondsignal that must be applied to said difference amplifier to reduce saiderror to zero.
 6. In combination, an edger roller drive for establishingan edger velocity Ve, main mill speed transducing means for producing arepresentation of main mill delivery speed Vd and mill deliverythickness Hd, a sequence control for producing a signal F/R representingforward and reverse mill passes, and automatic draft compensation meansresponsive to signal Hd, F/R and Vd for producing an edger velocityreference signal VEref for forward passes.
 7. The combination of claim 6wherein said automatic draft compensation means produces signal VErefaccording to the function: VEref Vd*Hd/He, where He is a signalrepresenting entry thickness for a forward pass and Hd represents theforward pass delivery thickness.
 8. The combination of claim 7 whereinsignal He is produced by storing a signal representing Hd in a memoryduring a reverse pass.
 9. The combination of claim 8 wherein signals Hdand He are represented by a screwdown position signal Sd measured in themain mill, with the memory of the screwdown position signal producedduring a reverse pass providing the representation of He for thefollowing forward pass.